When a weak female screw makes it impossible to obtain a high tightening force while directly tapping into a work comprising a light metal such as aluminum, plastics, or cast iron, it is the conventional practice to use a spiral coil insert for the purpose of compensate for a high reliable screw tightening.
There are a tanged spiral coil insert and a tangless spiral coil insert as a spiral coil insert, but the tanged spiral coil insert requires an operation of removing a tang, after being attached to a work, and further an operation of collecting the tang removed. Therefore, the tangless spiral coil insert, which does not require such operations, is occasionally used.
A patent literature 1 discloses an attachment tool for such a tangless spiral coil insert. This will be described below with reference to FIGS. 10 to 12 appended to the present patent application.
An attachment tool 300 is provided with a tubular member 301, and a mandrel assembly 302 supported by the tubular member 301. A pivotal claw 303 is disposed in a hollow 304 formed in a longitudinal direction of the mandrel assembly 302, and the pivotal claw 303 is provided with a hook section 305 engaging with a notch 101 (FIG. 12) of a tangless spiral coil insert 100 at one leading end thereof.
In this example, the pivotal claw 303 is biased about a pivotal shaft 307 by a spring 306, and, the pivotal claw 303 is configured to pivot on the pivotal shaft 307 so that the hook section 305 sinks into the notch 101 of the coil insert 100 when the mandrel assembly 302 moves in a direction of an arrow 308 and the other end 309 of the pivotal claw 303 has entered a hole formed in the mandrel assembly 302.